The present invention relates generally to data communications systems and more particularly relates to protocols for communicating with a programmable logic control device by sending a data sequence, typically one or more pages, via a forward overhead control channel of a cellular network control channel for a cellular mobile radiotelephone system.
In recent years, the communications industry has shown a growing interest in various types of wireless communications systems for communicating voice and/or data between numerous remote sites and a central location. It is well recognized that the use of a dedicated telephone facility for a conventional telephone system is not a convenient or economical option for all communications applications. For example, for many industrial applications, a central data collection site has a need for acquiring information from a variety of remotely located monitoring devices that collect data about the operation or performance of equipment. To overcome the limitations of the conventional telephone system, a two-way wireless communications link is often necessary to permit a response to a communication initiated from another location. In an attempt to solve the problem of supplying a response to an initial communication, the industry has offered various wireless communications systems, including two-way radios, cellular mobile radiotelephones, and paging systems.
To overcome the limitations of prior communications systems, the assignee for the present invention has developed a system for communicating data via a cellular network control channel of a cellular mobile radiotelephone (CMR) system. U.S. Pat. Nos. 5,526,401, 5,546,444, and 5,873,043, which are assigned to the assignee for the present application and contain subject matter fully incorporated herein by reference, describe an adapted use of the existing architecture of a CMR system in an efficient and cost-effective manner to support communications via the CMR system, including collection and reporting of data obtained at remote sites.
The data message system described in the referenced U.S. patents includes data reporting devices, at least one mobile switching center (MSC), and a data collection system connected directly or indirectly to the MSC or a Signal Transfer Point (STP). The MSC can issue commands or instructions, typically in a sequence of page messages, to the data reporting devices via the cellular network control channel of the CMR system. Each data reporting device can monitor the operation of a remote data source to collect selected data or can control the operation of a remote item in response to commands transmitted over the via the MSC. The data reporting device can transmit a data message containing the selected data via a cellular network control channel of the CMR system when the data reporting device first identifies itself or xe2x80x9cregistersxe2x80x9d for operation with the MSC. Alternatively, the data reporting device can send the selected data via the cellular network control channel in a data message formatted to represent a xe2x80x9ccall originationxe2x80x9d signal. In turn, the MSC can send the data message to the data collection system via a communications link. In this manner, the data message system takes advantage of an installed base of cellular communications equipment by using the cellular network control channel for data communications between a central location and one or more remote sites.
The data reporting device of the data message system typically communicates with the MSC via the reverse overhead control channel (RECC) of the cellular network control channel. In contrast, the MSC can communicate with a cellular-compatible device, such as a data reporting device, via the forward overhead control channel (FOCC) of the cellular network control channel. The conventional technique for sending a message to a cellular mobile radiotelephone from an MSC is the transmission of a page message over the FOCC. For example, a conventional cellular mobile radiotelephone can be stimulated by a transmission of the MSC to locate the mobile telephone unit when an incoming call from a landline has been placed to this unit. The data requirement for this type of trigger message is minimal for conventional cellular communications and, consequently, each message is independently processed as a complete data packet. This works well for the paging operations conducted by an MSC with conventional cellular mobile radiotelephones via the FOCC. However, this mechanism significantly limits the amount of information or instruction that can be provided by the MSC to a data reporting device via a page carried by the cellular network control channel. This is a disadvantage for applications requiring the communication of a commands and/or data via the CMR system to a remote cellular communications device for use by a controller, such as a programmable logic controller (PLC), coupled to a controllable item or instrument.
In view of the foregoing, there is a need for adapting the paging mechanism of a CMR system to support the transfer of commands and/or data for communications from an MSC to a cellular-compatible device. There is a further need for communicating with and controlling the operations of a remote controller, such as a PLC, coupled to a cellular-compatible device that can accept commands and/or data via the paging mechanism of a CMR system.
The present inventions solves the needs of the prior art by providing a method for communicating with cellular communication devices by sending multiple pages via a cellular network control channel of a cellular mobile radiotelephone (CMR) system. Each cellular communications device operating within the coverage area of the CMR system can monitor the Forward Overhead Control Channel (FOCC) of the cellular network control channel for a pair of pages, commonly described as target pages, within a first time period. Each target page includes a specific identifier assigned to one or more of the cellular communications devices. Each cellular communications device maintains a mask in memory for storing one or more specific identifiers assigned to that device. In the event that a cellular communications device receives a page, such as the target page, having a matching specific identifier, the device will complete an action responsive to that page. Otherwise, a cellular communications device will ignore a page having a specific identifier that does not match an identifier assigned to that device.
In response to receiving a pair of pages having a matching specific identifier within the first time period, typically 60 seconds, the cellular communications device monitors the cellular network control channel over a second time period for at least one data page having a predetermined characteristic designating the page as carrying data. For a data page formatted as a cellular telephony signal having a Mobile Identification Number (MIN) field, the predetermined characteristic can be defined as a 2, 3, 4, 5 or 6 positioned in the least significant digit (LSD) of the MIN carried by that page.
In response to receiving at least one data page having a predetermined characteristic during the second time period, the cellular communications device can collect the data carried by the received data page. This data can be stored at the cellular communications device for subsequent use or is forwarded for processing by another device, such as a programmable logic controller (PLC). To acknowledge receipt of the data, the cellular communications device can send an acknowledgement signal via the cellular network control channel. This acknowledgement signal can be formatted as a cellular telephony Autonomous Registration signal and carries an indication of data verification. A mobile switching center (MSC) typically receives the acknowledgement signal via the Reverse Overhead Control Channel (RECC) of the cellular network control channel.
For one aspect of the invention, the cellular communications device can continue to monitor the FOCC for a second consecutive data page if the predetermined characteristic in the first received data page specifies that a pair of consecutive pages carry data. This monitoring operation is typically carried out over the second time period. If the second data page is received during the second time period, then the cellular communications device can collect the data carried by both the first and second pages. The combination of data collected from the first and second pages can be forwarded by the cellular communications device to the PLC via a wired or wireless communications link. The cellular communications device can verify receipt of the data carried by both pages and issue an acknowledgement signal via the RECC to acknowledge receipt of such data. This acknowledgement signal can be formatted as an Autonomous Registration signal comprising an Acknowledge Pattern (AAA hex) within the upper 12 bits and collected data, represented in BCD, big-endian order format, within the lower 12 bits.
For another aspect of the invention, a cellular communications device can terminate monitoring operations prior to expiration of the second time period if the predetermined characteristic in the first received data page specifies that only a single page carries data. The cellular communications device can collect the data carried by the first data page and issue an acknowledgement signal via the RECC to acknowledge receipt of the data carried by that page. This acknowledgement signal can be formatted as an Autonomous Registration signal comprising an Acknowledge Pattern (AAAAAA hex) within the upper 24 bits and collected data represented in BCD, big endian order format, within the lower 8 bits.
The present invention also provides a method for communicating a programming command to a controller, such as a PLC, by sending multiple pages via the cellular network control channel of a CMR system. The PLC is typically coupled to a cellular communications device via a wired or wireless communications link. The cellular communications device can monitor the FOCC of the cellular network control channel for a target page having a specific identifier assigned to that communications device. Timely receipt of one or more target pages having a specific identifier assigned to the cellular communications device within a predetermined time period prompts that device to monitor the FOCC for a schedule page.
In response to receiving the target page(s), the cellular communications device can monitor for a time period the FOCC for a schedule page having a schedule command. The schedule command identifies a slot number in a look-up table maintained in memory by the PLC. This slot number represents a specific storage location within the look-up table for maintaining a programming command for the PLC.
In response to receiving the schedule page during the time period, the cellular communications device can forward the slot number to the PLC via the communications link. In turn, the PLC can retrieve from its look-up table the programming command identified by the slot number and initiate a program action associated with that programming command. The cellular communications device also can send an acknowledgement signal via the cellular network control channel to acknowledge receipt of the schedule command.
The present invention further provides a method for communicating a reprogramming command to a PLC by sending multiple pages via a cellular network control channel of the CMR system. A cellular communications device, which is coupled to the PLC, monitors the FOCC for one or more target pages having a specific identifier assigned to that device. In response to receiving target page(s) with a matching specific identifier during a time period, the cellular communication devices monitors the FOCC for a schedule page having a schedule command. The schedule command identifies a slot number specifying a particular stock in the PLC""s look-up table containing programming data. In response to receiving the schedule page during a time period, the cellular communications device monitors the FOCC for a data page carrying new programming data. Responsive to receiving the data page, the cellular communications devices forwards to the PLC the slot number and the new programming data. In addition, the cellular communications device sends an acknowledgement signal via the cellular network control channel to acknowledge receipt of the slot number and programming data.
In view of the foregoing, it will be understood that a cellular communications device operating within the coverage area of a CMR System can receive multiple pages via the FOCC and provide data extracted from one or more of these pages to a controller, such as PLC. The PLC, which is typically coupled to a controllable instrument, can accept the extracted data as programming data representing new or replacement program commands. In contrast to the prior art, the communication of programming data to a PLC requires the reception of multiple pages by a cellular communications device via the FOCC. These and other objectives of the present invention will become evident upon a review of the detailed description, the drawing set and the appended claim set.